Kink resistant stent-graft

ABSTRACT

A stent-graft including a stent member having an inner surface and an outer surface, a generally tubular graft member and a coupling member that couples the stent member to the graft member. The coupling member, which is the preferred embodiment is in the form of a ribbon, covers only a portion of the inner or outer surface of the stent member and secures the stent member and graft member to one another. Alternatively, the coupling member can be described as interconnecting less than entirely the inner or outer surface of the graft member to the stent member. With this construction, regions of the stent member do not interfere with the coupling member. Shear stresses between the stent member and the coupling member and the risk of tearing the graft or coupling member or delamination therebetween may be reduced as compared to a fully enveloped stent member. This construction also provides improved flexibility and kink resistance.

CONTINUING DATA

[0001] This is a continuation-in-part of prior application Ser. No.08/572,548, filed Dec. 14, 1995, the entirety of which is incorporatedherein by reference.

FIELD OF THE INVENTION

[0002] This invention relates generally to implants for repairing ductsand passageways in the body. More specifically, the invention relates toan expandable stent-graft.

BACKGROUND OF THE INVENTION

[0003] Treatment or isolation of vascular aneurysms or of vessel wallswhich have been thinned or thickened by disease has traditionally beenperformed via surgical bypassing with vascular grafts. Shortcomings ofthis procedure include the morbidity and mortality associated withsurgery, long recovery times after surgery, and the high incidence ofrepeat intervention needed due to limitations of the graft or of theprocedure.

[0004] Vessels thickened by disease are currently sometimes treated lessinvasively with intraluminal stents that mechanically hold these vesselsopen either subsequent to or as an adjunct to a balloon angioplastyprocedure. Shortcomings of current stents include the use of highlythrombogenic materials (stainless steels, tantalum, ELGILOY) which areexposed to blood, the general failure of these materials to attract andsupport functional endothelium, the irregular stent/vessel surface thatcauses unnatural blood flow patterns, and the mismatch of mechanicalcompliance and flexibility between the vessel and the stent.

[0005] Various attempts have been made to provide a nonthrombogenicblood-carrying conduit. Pinchuk, in U.S. Pat. Nos. 5,019,090, 5,092,887,and 5,163,958, suggests a spring stent which appears tocircumferentially and helically wind about as it is finally deployedexcept, perhaps, at the very end link of the stent. The Pinchuk '958patent further suggests the use of a pyrolytic carbon layer on thesurface of the stent to present a porous surface of improvedantithrombogenic properties.

[0006] U.S. Pat. No. 5,123,917, to Lee, suggests an expandable vasculargraft having a flexible cylindrical inner tubing and a number of“scaffold members” which are expandable, ring-like and providecircumferential rigidity to the graft. The scaffold members are deployedby deforming them beyond their plastic limit using, e.g., an angioplastyballoon.

[0007] A variety of stent-graft designs also have been developed toimprove upon simple stent configurations. Perhaps the most widely knownstent-graft is shown in Ersek, U.S. Pat. No. 3,657,744. Ersek shows asystem for deploying expandable, plastically deformable stents of metalmesh having an attached graft through the use of an expansion tool.

[0008] Palmaz describes a variety of expandable intraluminal vasculargrafts in a sequence of patents: U.S. Pat. Nos. 4,733,665; 4,739,762;4,776,337; and 5,102,417. The Palmaz '665 patent suggests grafts (whichalso function as stents) that are expanded using angioplasty balloons.The grafts are variously a wire mesh tube or of a plurality of thin barsfixedly secured to each other. The devices are installed, e.g., using anangioplasty balloon and consequently are not seen to be self-expanding.The Palmaz '762 and '337 patents appear to suggest the use ofthin-walled, biologically inert materials on the outer periphery of theearlier-described stents. Finally, the Palmaz '417 patent describes theuse of multiple stent sections each flexibly connected to its neighbor.

[0009] Rhodes, U.S. Pat. No. 5,122,154, shows an expandable stent-graftmade to be expanded using a balloon catheter. The stent is a sequence ofring-like members formed of links spaced apart along the graft. Thegraft is a sleeve of a material such as an expanded polyfluorocarbon,expanded polytetrafluoroethylene available from W. L. Gore & Associates,Inc. or IMPRA Corporation.

[0010] Schatz, U.S. Pat. No. 5,195,984, shows an expandable intraluminalstent and graft related in concept to the Palmaz patents discussedabove. Schatz discusses, in addition, the use of flexibly-connectingvascular grafts which contain several of the Palmaz stent rings to allowflexibility of the overall structure in following curving body lumen.

[0011] Cragg, “Percutaneous Femoropopliteal Graft Placement”, Radiology,vol. 187, no. 3, pp. 643-648 (1993), shows a stent-graft of aself-expanding, nitinol, zig-zag, helically wound stent having a sectionof polytetrafluoroethylene tubing sewed to the interior of the stent.

[0012] Cragg (European Patent Application 0,556,850) discloses anintraluminal stent made up of a continuous helix of zig-zag wire andhaving loops at each apex of the zig-zags. Those loops on the adjacentapexes are individually tied together to form diamond-shaped openingsamong the wires. The stent may be made of a metal such as nitinol (col.3 lines 15-25 and col. 4, lines 42+), and may be associated with a“polytetrafluoroethylene (PTFE), dacron, or any other suitablebiocompatible material”. Those biocompatible materials may be inside thestent (col. 3 lines 52+) or outside the stent (col. 4, lines 6+).

[0013] WO93/13825 to Maeda et al. discloses a self-expanding stenthaving a wire bent into an elongated zig-zag pattern and helically wouldabout a tubular shape interconnected with a filament. A sleeve may beattached to the outer or inner surface of the stent.

[0014] PCT application publication WO/95/05132 discloses a stent-graftwith a tubular diametrically adjustable stent.

[0015] There is a need for an alternate stent-graft construction thatexhibits excellent kink resistance and flexibility.

SUMMARY OF THE INVENTION

[0016] The present invention involves a stent-graft including a stentmember having an inner surface and an outer surface, a generally tubulargraft member and a coupling member that couples the stent member to thegraft member. The coupling member, which in the preferred embodiment isin the form of a ribbon, covers only a portion of at least one of theinner or outer surface of the stent member and secures the stent memberand graft member to one another. Alternatively, the coupling member canbe described as interconnecting less than entirely the inner or outersurface of the stent member to the graft member.

[0017] With this construction, regions of the stent member do notinterface with the coupling member. This is believed to advantageouslyreduce shear stresses between the stent member and the coupling memberwhen the stent-graft undergoes bending so that tearing of the couplingand/or graft member can be minimized or eliminated. It is also believedthat this arrangement minimizes the likelihood of delamination betweenthe coupling member and the graft. If delamination were to occur, theinner portion of the stent-graft could perceivable collapse into thevessel lumen and interfere with desired blood flow. Thus, thestent-graft is believed to be capable of conforming to curves in a bloodvessel lumen with minimal risk of tearing the graft or coupling member,or delamination between the stent and graft members.

[0018] According to another aspect of the invention, the coupling memberis secured to the graft member without sutures. When the graft member isplaced within the stent member, for example, this arrangement eliminatesthe need for having sutures extend into the lumen formed by the graftmember and possibly interfere with blood flow. Another benefit of thisarrangement, as compared to suturing the stent to the graft member, isthat suture holes need not be placed in the graft which could adverselyaffect its integrity. The coupling member may be thermally or adhesivelybonded to the graft member.

[0019] The coupling member preferably has a generally broad or flatworking surface as compared to filament or thread-like structures suchas sutures. As noted above, a preferred coupling member is in the formof a ribbon. This configuration advantageously increases potentialbonding surface area between the coupling member and the graft member toenhance the integrity of the bond therebetween. The increased bondingsurface may facilitate minimizing the thickness of the coupling memberso that the stent-graft Patent lumen volume and blood flow dynamicstherein can be optimized. For example, a thicker coupling member wouldincrease the overall stent-graft thickness which can cause anundesirable lumen diameter reduction at the transition where the vessellumen interfaces the inlet of the stent-graft. This, in turn, can resultin undesirable turbulent flow which possibly can lead to complicationssuch as thrombosis.

[0020] According to a preferred embodiment of the invention, thecoupling member is arranged in a helical configuration with multipleturns. Each of a number of the coupling member turns is spaced from theturn(s) adjacent thereto. With this construction, a generally uniformdistribution of coupling member-free stress relief zones may beachieved. Elastic wrinkling in the graft member may occur in those zonesso that the graft member can absorb stress when bent along itslongitudinal axis, for example, and resist kinking.

[0021] According to a preferred stent member construction for use withthe stent-graft of the present invention, at least a portion of thestent member includes undulations and is arranged in a helicalconfiguration with multiple turns. Each stent member undulation includesan apex and an open base portion. The apexes and base portions areconfigured so as not to restrain one apex into the undulation in anadjacent turn and substantially in-phase therewith when the stent-graftis bent or compressed. This is believed to facilitate undulationmovement during bending or compression and minimize the likelihood ofstress build-up that may cause kinking. The coupling member typicallycovers a substantial portion of each undulation so as to minimize thelikelihood of the stent member apexes bending away from the graft memberand interfering with the environment or tether line which may be used tomaintain the stent-graft in a folded state before deployment. Thecoupling member also may be positioned adjacent to the apexes tominimize the likelihood of such apex movement.

[0022] According to another aspect of the invention, the end portions ofthe stent-member also may be enveloped between the coupling member ordiscrete coupling members and the graft member. This prevents theterminal portions of the stent and graft members from significantlymoving away from one another. For example, when the stent-member isexternal to the graft member, the terminal graft portions may flap awayfrom the stent member and possibly interfere with blood flow if theterminal coupling portions were not present.

[0023] According to another feature of the invention, the stent-graft isadvantageously manufactured by placing a cushioning layer around amandrel, assembling the stent-graft on the cushioning layer, surroundingthe mandrel mounted assembly with a multi-component member formed from aPTFE tube having a longitudinal slit and which is wrapped with anexpanded PTFE or other film or tape to compress the assembly, andheating the assembly to bond a coupling member to the graft.

[0024] The above is a brief description of some deficiencies in theprior art, and advantages and aspects of the present invention. Otherfeatures, advantages, and embodiments of the invention will be apparentto those skilled in the art from the following description, accompanyingdrawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1A is a perspective view of a stent-graft constructed inaccordance with the principles of the present invention.

[0026]FIG. 1B is an enlarged perspective view of a mid-portion of thestent-graft shown in FIG. 1A.

[0027]FIG. 1C is an enlarged perspective view of a portion of thestent-graft shown in FIG. 1A mounted on a cushioned mandrel.

[0028]FIG. 2 is a side view of an enlarged portion of the stent-graftshown in FIG. 1A

[0029]FIG. 3A is a diagrammatic representation of a transverse sectionof the stent-graft of FIG. 1 prior to the coupling and graft membersbeing secured to one another.

[0030]FIG. 3B is an enlarged portion of the section shown in FIG. 3Aafter the coupling and graft members have been secured to one another.

[0031]FIG. 4 illustrates the stent-graft of FIGS. 1A & 1B underlongitudinal, axial compression.

[0032]FIG. 5 is a sectional view of the stent-graft of FIGS. 1A and 1Btaken along line 5-5 in FIG. 4.

[0033]FIG. 6 diagrammatically shows a portion of the stent-graft ofFIGS. 1A and 1B bent along its longitudinal axis.

[0034]FIG. 7 is a perspective view of another embodiment of thestent-graft of the present invention having an alternate stent to graftcoupling configuration.

[0035]FIG. 8 is a side view of an enlarged portion of the stent-graftshown in FIG. 7.

[0036]FIG. 9 is a perspective view of a further embodiment of thestent-graft of the present invention having yet another stent to graftcoupling.

[0037]FIG. 10 is a side view of an enlarged portion of the stent-graftshown in FIG. 9.

[0038]FIG. 11 is a partial view of the stent-graft of FIG. 1A showing anend portion of the device.

[0039]FIG. 12 is an abstracted portion of a suitable stent and shows theconcept of torsion on a portion of that stent.

[0040]FIG. 13A diagrammatically shows a further stent-member of thepresent invention with flared ends (the coupling tape drawn back to moreclearly show the helically wound undulating stent configuration).

[0041]FIG. 13B diagrammatically shows a further stent-memberconstruction for supporting the graft member.

[0042]FIGS. 14A, 14B, 14C, 14D, 14E, and 14F are plan views of unrolledstent forms suitable for use in the invention.

[0043]FIGS. 15A, 15C and 15E show procedures for folding thestent-grafts. FIGS. 15B, 15D, and 15F show the corresponding foldedstent-grafts.

[0044]FIGS. 16A, 16B, and 16C diagrammatically show a procedure fordeploying the stent-grafts using an external sleeve.

[0045]FIGS. 17A and 18A are partial perspective views of foldedstent-grafts. FIGS. 17B, 18C, 18B, and 18C are end views of thestent-grafts shown in FIGS. 17A and 18A in folded and open states.

[0046]FIGS. 19A, 19B, and 19C diagrammatically show a procedure fordeploying the stent-grafts shown in FIGS. 17A17C and 18A-18C using atether wire.

[0047] FIGS. 20 show a close-up view of a stent fold line using apreferred sack knot in the slip line.

[0048]FIG. 21 is a diagrammatic perspective view of a folded stent-graftheld in a position by a tether line and a sack knot as illustrated inFIG. 20.

[0049]FIGS. 22, 23, 24, and 25 are diagrammatic sequential illustrationsof a further deployment procedure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] Referring to the drawings in detail wherein like numbers indicatelike elements, an expandable stent-graft 2 is shown constructedaccording to the principles of the present invention. Althoughparticular stent and graft constructions will be described inconjunction with the preferred embodiments, it should be understood thatother constructions may be used without departing from the scope of theinvention.

[0051] Referring to FIGS. 1A and B, stent-graft 2 generally includes athin-walled tube or graft member 4, a stent member 6 and a couplingmember 8 for coupling the stent and graft members together. Preferably,the stent and graft members are coupled together so that they aregenerally coaxial.

[0052] Tubular expandable stent member 6 is generally cylindrical andcomprises a helically arranged undulating member 10 having plurality ofhelical turns 12 and preferably comprising nitinol wire. The undulationspreferably are aligned so that they are “in-phase” with each other asshown in FIGS. 1A and 1B, for example. More specifically, undulatinghelical member 10 forms a plurality of undulations 14, each including anapex portion 16 and a base portion 18. When the undulations arein-phase, apex portions 16 in adjacent helical turns 12 are aligned sothat an apex portion 16 may be displaced into a respective base portion18 of a corresponding undulation in-phase therewith and in an adjacenthelical turn.

[0053] Once the undulations are aligned so that adjacent undulations inone turn are in-phase with the undulations in the helical turns adjacentthereto, a linking member 20 may be provided to maintain the phasedrelationship of the undulations during compression and deployment, andduring bending of the stent member. In the illustrative embodiment,linking member 20 is laced or interwoven between undulations in adjacentturns of the helical member and acquires a helical configuration (See,e.g., FIGS. 1-3). Linking member 20 preferably comprises a biocompatiblepolymeric or metallic material having sufficient flexibility to bereadily folded upon itself.

[0054] Undulations 14 preferably are unconfined in that they areconfigured so as not to tend to inhibit the movement of flexible link 20down between respective torsion arms or lengths 22 a and 22 b. Inaddition, the undulations preferably are configured and arranged so thata respective apex portion can readily move within a correspondingundulation base portion 18 in-phase therewith. It is believed that thisconstruction minimizes the likelihood of stress build-up, for example,during bending or compression (as depicted in the lower portion of FIG.6) and, thus, improves the kink resistance of the stent-graft.

[0055] Referring to FIGS. 3A and 3B, stent member 6 is disposed betweengenerally tubular graft member 4 and coupling member 8. The stent memberprovides a support structure for the graft member to minimize thelikelihood of the graft member collapsing during use. Although the graftmember may surround the outer surface of the stent member, it preferablyis placed within the stent member to provide a relatively smooth(wrinkles may form in the graft member between coupling member turnsduring compression) intralumental stent-graft surface as shown in thedrawings.

[0056] An important aspect of the invention is that the coupling member,which secures the stent member to the graft member, covers only aportion of the stent member. Alternatively, the coupling member can bedescribed as preferably interconnecting less than entirely the inner orouter surface of the stent member to the graft member (e.g., it coversless than all of the outer surface of the stent member when the graftmember is positioned inside the stent member). With this construction,regions of the stent member do not interface with the coupling memberwhen the stent-graft is an uncompressed state, for example. This isbelieved to advantageously reduce shear stresses between the stentmember and the coupling member when the stent-graft undergoes bending orcompression, thereby reducing the risk of tearing the graft or couplingmember or causing delamination between the stent and graft members.

[0057] The coupling member also preferably has a generally broad or flatsurface for interfacing with the stent and graft members as compared tofilament or threadlike structures such as sutures. This increasespotential bonding surface area between the coupling member and the graftmember to enhance the structural integrity of the stent-graph. Theincreased bonding surface area also facilitates minimizing the thicknessof the coupling member. It has been found that a coupling member in aform of a generally flat ribbon or tape as shown in the drawings anddesignated with reference numeral 8, provides the desired results.

[0058] As noted above, coupling member 8 preferably is in the form of agenerally flat ribbon or tape having at least one generally flatsurface. In addition, coupling member 8 is arranged in a helicalconfiguration according to the preferred embodiments illustrated in thedrawings. Referring to FIG. 2, helically arranged coupling member 8 isformed with multiple helical turns 23, each being spaced from the turnsadjacent thereto, thereby forming coupling member-free stress reliefzones 24 between adjacent turns. The coupling member also preferably isarranged to provide a generally uniform distribution of stress reliefzones 24. In the illustrated embodiments, coupling member 8 is helicallywound around the stent member with its helical turns 23 aligned with thestent member turns 12. As shown, the coupling member may be constructedwith a constant width and arranged with uniform spacing between turns.

[0059] Coupling member 8 also preferably covers a substantial portion ofeach undulation so as to minimize the likelihood of the stent memberapexes lifting away from the graft member and interfering with theirimmediate environment. Coupling members having widths of 0.025, 0.050and 0.075 inches have been applied to the illustrated stent memberhaving a peak-to-peak undulation amplitude of about 0.075 inch withsuitable results. However, it has been found that as the coupling memberband width increases, the stent-graft flexibility generally isdiminished. It is believed that coupling member width of about one-forthto three-fourths the amplitude of undulations 14, measured peak-to-peak,is preferred (more preferably about one third to two thirds thatamplitude) to optimize flexibility. It also has been found that bypositioning one of lateral margins of the ribbon-shaped coupling member8 adjacent to the apexes, e.g., in abutment with linking member 20, thecoupling member width may be reduced without significantly sacrificingapex securement. Varying the width of the coupling member can alsoresult in the adjustment of other structural properties. Increasing thewidth can also potentially increase the radial stiffness and the burstpressure and decrease the porosity of the device. Increasing band widthcan also diminish graft member wrinkling between coupling member turns.

[0060] Coupling member 8 (or separate pieces thereof) also surrounds theterminal end portions of the stent-graft to secure the terminal portionsof the graft member to the support structure formed by stent member 6 asshown in FIG. 11, for example.

[0061] Although the coupling member may cover a substantial portion ofeach undulation as discussed above, apex portions 16 may still movewithin the undulations in-phase therewith as shown in FIGS. 4-6 dueprimarily to the flexibility of coupling and linking members 8 and 20respectively. Further, coupling member 8 may be wrapped so as to becompletely external to stent member 6 as shown in FIGS. 1-6, interwovenabove and below alternating undulations 14 as shown in FIGS. 7 and 8, orinterwoven above and below alternating undulation arms 22 a and 22 b asshown in FIGS. 9 and 10. In addition, the ribbon-shaped tape or couplingmember 8 may be axially spaced away from the apexes and linking member20 (FIGS. 9 and 10) as compared to the embodiments shown in FIGS. 1-8.This spacing provides an area 28 in which linking member 20 can freelymove without restraint, thereby reducing any resistance placed on apexesmoving into corresponding undulations during compression or bending.

[0062] The coupling member 8 may be wrapped (placed) on or interwovenwith the undulations of the stent before or after it is positionedaround the graft. For example the coupling member may be placed on orinterwoven with the undulations of element 10 of FIG. 14A. As a resultof fluorinated ethylene propylene (FEP) coating on a surface of thecoupling member, element 10 will be bonded to the coupling member byheating. The resulting element is then configured into the stent of thisinvention. Placing or wrapping the coupling member is performed in amanner similar to that described and shown for FIGS. 1-11.

[0063] Although a particular coupling member configuration and patternhas been illustrated and described, other configuration and/or patternsmay be used without departing from the scope of the present invention.For example, coupling member(s) arranged in a multiple helix (e.g., adouble or triple helix) may be used. Longitudinally extending strips ofribbon may be used and may be preferred when the coupling member is usedin conjunction with other stent member configurations.

[0064] Each undulation 14 alternatively may be described as a torsionsegment and for purposes of the following discussion will be referred toas a torsion segment 14. Referring to FIG. 12, an isolated undulation 14is shown to facilitate the following discussion involving stentmechanics involved in deployment of the device. Each torsion segmentincludes an apex portion 16 and two adjacent torsion arms or lengths 22a and 22 b extending therefrom. Typically, then, each torsion arm 22 a &b will be a component of each of two adjacent torsion segments 14. Whentorsion segment 14 undergoes a flexing in the amount of α° apex portion16 will flex some amount β°, torsion arm 22 a will undertake a twist ofγ° and torsion arm 22 b will undertake a twist opposite of that found intorsion arm 22 a in the amount of δ°. The amounts of angular torsionfound in the torsion arms (22 a & 22 b) will not necessarily be equalbecause the torsion arms will not necessarily be equal because thetorsion arms are not necessarily at the same angle to the longitudinalaxis of the stent-member. Nevertheless, the sum of β°+γ°+δ° will equalα°. When a value of α° is chosen, as by selection of the shape and sizeof the stent-member upon folding, the values of the other three angles(β°, γ°, δ°) are chosen by virtue of selection of number or torsionsegments around the stent, size and physical characteristics of thewire, and length of the torsion areas (22 a & b). Each of the notedangles must not be so large as to exceed the values at which the chosenmaterial of construction plastically deforms at the chosen value of α°.

[0065] To further explain: it should be understood that torsion segment14 undergoes a significant amount of flexing as the stent-member isfolded or compressed in some fashion. The flexing provides a twist tothe torsion arms (22 a & b), a significant portion of which is generallyparallel to the longitudinal axis of the stent.

[0066] The described stent-member uses concepts which can be thought ofas widely distributing and storing the force necessary to fold thetubular stent into a configuration which will fit through a diametersmaller than its relaxed outside diameter without inducing plasticdeformation of the constituent metal or plastic and yet allowing thosedistributed forces to expand the stent upon deployment.

[0067] Once the concept of distributing the folding or compressionstresses both into a bending component (as typified by angle β° in FIG.12) and to twisting components (as typified by angle γ° and δ° in FIG.12) and determining the overall size of a desired stent, determinationof the optimum materials as well as the sizes of the various integralcomponents making up the stent becomes straightforward. Specifically,the diameter and length of torsion lengths, apex portion dimensions andthe number of torsion segments around the stent may then be determined.

[0068] Referring to FIG. 13A, a stent-graft^(iv) differing fromstent-graft 1 in graft support structure is shown. Stent-graft 2 ^(iv)includes stent member 6′ which is the same as stent member 6 with theexception that it includes flared end portions 142 at one or both ends.Flared end portions 142 provide secure anchoring of the resultingstent-graft 2 ^(iv) against the vessel wall and prevents the implantfrom migrating downstream. In addition, flared end portions 142 providea tight seal against the vessel so that the blood is channeled throughthe lumen rather than outside the graft. The undulating structure mayvary in spacing to allow the helical turns to maintain their phasedrelationship as discussed above. Although a linking member between thecontinuous helical turns is not shown, such structure preferably isincluded to maintain the alignment of the apexes as discussed above.

[0069] The graft support structure also may be made by forming a desiredstructural pattern out of a flat sheet. The sheet may then be rolled toform a tube. The stent also may be machined from tubing. If the chosenmaterial is nitinol, careful control of temperature during the machiningstep may be had by EDM (electro-discharge-machining), laser cutting,chemical machining, or high pressure water cutting. As shown in FIG.13B, the stent-member (graft support structure) may comprise multipletubular members or sections 50, each coupled to the graft-member 4 witha coupling member as described above. Tubular members or sections 50 mayhave various construction and, thus, may be configured to have the sameconstruction as the stent-member 6 shown in FIGS. 1-11, for example.Tubular members also may be directly coupled to each other (e.g., withbridging element(s) extend between adjacent sections as would beapparent to one of ordinary skill) or, indirectly coupled to each otherthrough their interconnection with the graft member.

[0070] Referring to FIGS. 14A-F, various undulation configurationssuitable for the present invention are shown. FIG. 14A shows thesinusoidal shaped undulating member 10 described above. Adjacent torsionarms 22 a & b are not parallel. FIG. 14B shows an undulating member 10′having generally U-shaped undulations or torsion members where thetorsion arms are generally parallel. FIG. 14C shows a further variationwhere undulating member 10″ includes ovoid shaped undulations or torsionsegments. In this variation, adjacent torsion arms 22″a & b are againnot parallel, but generally form an open-ended oval. FIG. 14D showsanother variation where undulating member 10″′ includes V-shaped torsionmembers. In this variation, the adjacent torsion arms 120 form arelatively sharp angle at the respective apex portions. FIG. 14E shownundulating member 10 ^(iv) in which adjacent undulations have differentamplitudes. The peaks of the large amplitude torsion segments 119 may belined up “out of phase” or “peak to peak” with small or large amplitudetorsion segments 110, 121, respectively, in the adjacent turn of thehelix or may be positioned “in phase” similar to those discussed withregard to FIGS. 1A and B above. The configurations shown in FIGS.14A-14E are exceptionally kink-resistant and flexible when flexed alongthe longitudinal axis of the stent-member. FIG. 14F shows a stent formedfrom sections 11 and 13 which are connected to one another by sutures15.

[0071] As discussed above, the stent member preferably is orientedcoaxially with the tubular graft member. Although the stent member maybe placed within the graft member, it preferably is placed on the outersurface of the graft member so that a relatively smooth graft wallinterfaces with the blood. In certain configurations, an additionalgraft member may be placed on the outer surface of the stent-graftillustrated in the drawings. When the multiple graft structure isutilized, the stent structure should have the strength and flexibilityto urge the graft tubing firmly against the vessel wall so that thegraft member conforms with the inner surface of the vessel wall. Inaddition, the graft member preferably is impermeable to blood at normalor physiologic blood pressures. The impermeability makes the stent-graftsuitable for shunting and thereby hydraulically isolating aneurysms.

[0072] The scope of materials suitable for the stent and graft membersand the linking member as well as deployment mechanisms will bediscussed in detail, below.

[0073] Stent Materials

[0074] The stent member is constructed of a reasonably high strengthmaterial, i.e., one which is resistant to plastic deformation whenstressed. Preferably, the stent member comprises a wire which ishelically wound around a mandrel having pins arranged thereon so thatthe helical turns and undulations can be formed simultaneously. Otherconstructions also may be used. For example, an appropriate shape may beformed from a flat stock and wound into a cylinder or a length of tubingformed into an appropriate shape.

[0075] In order to minimize the wall thickness of the stent-graft, thestent material should have a high strength-to-volume ratio. Use ofdesigns as depicted herein provides stents which may be longer in lengththan conventional designs. Additionally, the designs do not suffer froma tendency to twist (or helically unwind) or to shorten as thestent-graft is deployed. As will be discussed below, materials suitablein these stents and meeting these criteria include various metals andsome polymers.

[0076] A percutaneously delivered stent-graft must expand from a reduceddiameter, necessary for delivery, to a larger deployed diameter. Thediameters of these devices obviously vary with the size of the bodylumen into which they are placed. For instance, the stents of thisinvention may range in size from 2.0 mm in diameter (for neurologicalapplications) to 40 mm in diameter (for placement in the aorta). A rangeof about 2.0 mm to 6.5 mm (perhaps to 10.0 mm) is believed to bedesirable. Typically, expansion ratios of 2:1 or more are required.These stents are capable of expansion ratios of up to 5:1 for largerdiameter stents. Typical expansion ratios for use with the stents-graftsof the invention typically are in the range of about 2:1 to about 4:1although the invention is not so limited. The thickness of the stentmaterials obviously varies with the size (or diameter) of the stent andthe ultimate required yield strength of the folded stent. These valuesare further dependent upon the selected materials of construction. Wireused in these variations are typically of stronger alloys, e.g., nitinoland stronger spring stainless steels, and have diameters of about 0.002inches to 0.005 inches. For the larger stents, the appropriate diameterfor the stent wire may be somewhat larger, e.g., 0.005 to 0.020 inches.For flat stock metallic stents, thickness of about 0.002 inches to 0.005inches is usually sufficient. For the larger stents, the appropriatethickness for the stent flat stock may be somewhat thicker, e.g., 0.005to 0.020 inches.

[0077] The stent-graft is fabricated in the expanded configuration. Inorder to reduce its diameter for delivery the stent-graft would befolded along its length, similar to the way in which a PCTA balloonwould be folded. It is desirable, when using super-elastic alloys whichalso have temperature-memory characteristics, to reduce the diameter ofthe stent at a temperature below the transition-temperature of thealloys. Often the phase of the alloy at the lower temperature issomewhat more workable and easily formed. The temperature of deploymentis desirably above the transition temperature to allow use of thesuper-elastic properties of the alloy.

[0078] There are a variety of disclosures in which super-elastic alloyssuch as a nitinol are used in stents. See, U.S. Pat. Nos. 4,503,569 toDotter, 4,512,338 to Balko et al., 4,990,155 to Wilkoff, 5,037,427 toHarada, et al., 5,147,370 to MacNamara et al., 5,211,658 to Clouse, and5,221,261 to Termin et al. None of these references suggest a devicehaving discrete individual, energy-storing torsional members.

[0079] Jervis, in U.S. Pat. Nos. 4,665,906 and 5,067,957, describes theuse of shape memory alloys having stress-induced martensite propertiesin medical devices which are implantable or, at least, introduced intothe human body.

[0080] It should be clear that a variety of materials variouslymetallic, superelastic alloys, and preferably nitinol, are suitable foruse in these stents. Primary requirements of the materials are that theybe suitably springy even when fashioned into very thin sheets or smalldiameter wires. Various stainless steels which have been physically,chemically, and otherwise treated to produce high springiness aresuitable, as are other metal alloys such as cobalt chrome alloys (e.g.,ELGILOY), platinum/tungsten alloys, and especially the nickel-titaniumalloys generically known as “nitinol”.

[0081] Nitinol is especially preferred because of its “super-elastic” or“pseudo-elastic” shape recovery properties, i.e., the ability towithstand a significant amount of bending and flexing and yet return toits original form without deformation. These metals are characterized bytheir ability to be transformed from an austenitic crystal structure toa stress-induced martensitic structure at certain temperatures, and toreturn elastically to the austenitic shape when the stress is released.These alternating crystalline structures provide the alloy with itssuper-elastic properties. These alloys are well known but are describedin U.S. Pat. Nos. 3,174,851, 3,351,463, and 3,753,700. Typically nitinolwill be nominally 50.6% (±0.2%) Ni with remainder Ti. Commerciallyavailable nitinol materials usually will be sequentially mixed, cast,formed, and separately cold-worked to 30-40%, annealed, and stretched.Nominal, ultimate yield strength values for commercial nitinol are inthe range of 30 psi and for Young's modulus are about 700 Kbar.

[0082] The '700 patent describes an alloy containing a higher ironcontent and consequently has a higher modulus than the Ni—Ti alloys.

[0083] Nitinol is further suitable because it has a relatively highstrength to volume ratio. This allows the torsion members to be shorterthan for less elastic metals. The flexibility of the stent-graft islargely dictated by the length of the torsion segments and/or torsionarms. The shorter the pitch of the device, the more flexible thestent-graft structure can be made. Materials other than nitinol aresuitable. Spring tempered stainless steels and cobalt-chromium alloyssuch as ELGILOY are also suitable as are a wide variety of other known“super-elastic” alloys.

[0084] Although nitinol is preferred in this service because of itsphysical properties and its significant history in implantable medicaldevices, we also consider it also to be useful in a stent because of itsoverall suitability with magnetic resonance imaging (MRI) technology.Many other alloys, particularly those based on iron, are an anathema tothe practice of MRI causing exceptionally poor images in the region ofthe alloy implant. Nitinol does not cause such problems.

[0085] Other materials suitable as the stent include certain polymericmaterials, particularly engineering plastics such as thermotropic liquidcrystal polymers (“LCP's”). These polymers are high molecular weightmaterials which can exist in a so-called “liquid crystalline state”where the material has some of the properties of a liquid (in that itcan flow) but retains the long range molecular order of a crystal. Thereterm “thermotropic” refers to the class of LCP's which are formed bytemperature adjustment. LCP's may be prepared from monomers such asp,p′hydroxy-polynuclear-aromatics or dicarboxy-polynuclear-aromatics.The LCP's are easily formed and retain the necessary interpolymerattraction at room temperature to act as high strength plastic artifactsas are needed as a foldable stent. They are particularly suitable whenaugmented or filled with fibers such as those of the metals or alloysdiscussed below. It is to be noted that the fibers need not be linearbut may have some preforming such as corrugations which add to thephysical torsion enhancing abilities of the composite.

[0086] Linkinq Member Materials

[0087] Flexible link 20, which is slidably disposed between adjacentturns of the helix may be of any appropriate filamentary material whichis blood compatible or biocompatible and sufficiently flexible to allowthe stent to flex and not deform the stent upon folding. Although thelinkage may be a single or multiple strand wire (platinum,platinum/tungsten, gold, palladium, tantalum, stainless steel, etc.),much preferred in this invention is the use of polymeric biocompatiblefilaments. Synthetic polymers such as polyethylene, polypropylene,polyurethane, polyglycolic acid, polyesters, polyamides, their mixtures,blends and copolymers are suitable; preferred of this class arepolyesters such as, polyethylene terephthalate including DACRON andMYLAR and polyaramids such as KEVLAR, polyfluorocarbons such aspolytetrafluoroethylene with and without copolymerizedhexafluoropropylene, TEFLON or ePTFE, and porous or nonporouspolyurethanes. Natural materials or materials based on natural sourcessuch as collagen may also be used in this service.

[0088] Graft Member Materials

[0089] The tubular component or graft member of the stent-graft may bemade up of any material which is suitable for use as a graft in thechosen body lumen. Many graft materials are known, particularly knownare those used as vascular graft materials. For instance, naturalmaterials such as collagen may be introduced onto the inner surface ofthe stent and fastened into place. Desirable collagen-based materialsinclude those described in U.S. Pat. No. 5,162,430, to Rhee et al, andWO 94/01483 (PCT/US93/06292), the entirety of which are incorporated byreference. Synthetic polymers such as polyethylene, polypropylene,polyurethane, polyglycolic acid, polyesters, polyamides, their mixture,blends, copolymers, mixtures, blends and copolymers are suitable,preferred of this class are polyesters such as polyethyleneterephthalate including DACRON and MYLAR and polyaramids such as KEVLAR,polyfluorocarbons such as polytetrafluoroethylene (PTFE) with andwithout copolymerized hexafluoropropylene, expanded or not-expandedPTFE, and porous or nonporous polyurethanes. Especially preferred inthis invention are the expanded fluorocarbon polymers (especially PTFE)materials described in British Pat. Nos. 1,355,373, 1,506,432, or1,506,432 or in U.S. Pat. Nos. 3,953,566, 4,187,390, or 5,276,276, theentirety of which are incorporated by reference.

[0090] Included in the class of preferred fluoropolymers arepolytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP),copolymers of tetrafluorethylene (TFE), and perfluoro (propyl vinylether) (PFA), homopolymers of polychlorotrifluoroethylene (PCTFE), andits copolymers with TFE, ethylene-chlorotrifluoroethylene (ECTFE),copolymers of ethylene-tetrafluoroethylene (ETFE), polyvinylidenefluoride (PVDF), and polyvinyfluoride (PVF). Especially preferred,because of its widespread use in vascular protheses, is expanded PTFE.

[0091] In addition, one or more radio-opaque metallic fibers, such asgold, platinum, platinum-tungsten, palladium, platinum-iridium, rhodium,tantalum, or alloys or composites of these metals like may beincorporated into the device, particularly, into the graft, to allowfluoroscopic visualization of the device.

[0092] The tubular component may also be reinforced using a network ofsmall diameter fibers. The fibers may be random, braided, knitted orwoven. The fibers may be imbedded in the tubular component, may beplaced in a separate layer coaxial with the tubular component, or may beused in a combination of the two.

[0093] A preferred material for the graft and coupling members is porousexpanded polytetrafluorethylene. An FEP coating is one preferredadhesive that is provided on one side of the coupling member.

[0094] Manufacture of the Stent-Graft

[0095] The following example is provided for purposes of illustrating apreferred method of manufacturing a stent-graft constructed according tothe present invention which in this example case is the stent-graftshown in FIGS. 1-6. It should be noted, however, that this example isnot intended to limit the invention.

[0096] The stent member wire is helically wound around a mandrel havingpins positioned thereon so that the helical structure and undulationscan be formed simultaneously. While still on the mandrel, the stentmember is heated to about 460° F. for about 20 minutes so that itretains its shape.

[0097] Wire sizes and materials may vary widely depending on theapplication. The following is an example construction for a stent-graftdesigned to accommodate 6 mm diameter vessel lumen. The stent membercomprises a nitinol wire (50.8 atomic % Ni) having a diameter of about0.007 inch. In this example case, the wire is formed to have sinusoidalundulations, each having an amplitude measured peak-to-peak of about0.100 inch and the helix is formed with a pitch of about 10 windings perinch. The inner diameter of the helix (when unconstrained) is about 6.8mm. The nitinol wire may be polished if desired. If a polished wire isdesired, the wire is fed through an electrolytic bath having an appliedpotential to electrolytically clean, passivate and polish the wire. Thepolishing reduces the availability of surface nickel for extraction orcorrosion. Suitable electrolytic treating materials for the bath arecommercially available. One such source of a commercially availableelectrolytic treating material is NDC (Nitinol Devices and Components.The linking member can be arranged as shown in the drawings and may havea diameter of about 0.006 inch.

[0098] In this example, the graft member is porous expandedpolytetrafluorethylene (PTFE), while the coupling member is expandedPTFE coated with FEP. The coupling member is in the form of a flatribbon (as shown in the illustrative embodiments) that is positionedaround the stent and graft members as shown in FIGS. 1-3. The side ofthe coupling member or ribbon that is FEP coated faces the graft memberto secure it to the graft member. The intermediate stent-graftconstruction is heated to allow the materials of the ribbon and graftmember to merge and self-bind as will be described in more detail below.

[0099] The FEP-coated porous expanded PTFE film used to form the ribbonshaped coupling member preferably is made by a process which comprisesthe steps of:

[0100] (a) contacting a porous PTFE film with another layer which ispreferably a film of FEP or alternatively of another thermoplasticpolymer.

[0101] (b) heating the composition obtained in step (a) to a temperatureabove the melting point of the thermoplastic polymer;

[0102] (c) stretching the heated composition of step (b) whilemaintaining the temperature above the melting point of the thermoplasticpolymer, and

[0103] (d) cooling the product of step (c)

[0104] In addition to FEP, other thermoplastic polymers includingthermoplastic fluoropolymers may also be used to make this coated film.The adhesive coating on the porous expanded PTFE film may be eithercontinuous (non-porous) or discontinuous (porous) depending primarily onthe amount and rate of stretching, the temperature during stretching,and the thickness of the adhesive prior to stretching.

[0105] The thin wall expanded PTFE graft used to construct this examplecontains an inner tube of PTFE and an outer helical wrap of PTFE. Thegraft was about 0.1 mm (0.004 in) thickness and had a density of about0.5 g/cc. The microstructure of the porous expanded PTFE containedfibrils of about 25 micron length. A 3 cm length of this graft materialwas placed on a mandrel the same diameter as the inner diameter of thegraft. Advantageously, as shown in FIG. 1C, a cushioning layer 5 wasplaced on the mandrel 3 prior to placement of the graft 4. The nitinolstent member having about a 3 cm length was then carefully fitted overthe center of the thin wall graft 4 and extended to its desired length.Any struts out of phase should be placed in phase prior to applying thecoupling member.

[0106] The stent-member was then provided with a ribbon shaped couplingmember comprised of the FEP coated film as described above. The couplingmember was helically wrapped around the exterior surface of thestent-member as shown in FIGS. 1-6. The uniaxially-oriented fibrils ofthe microstructure of the helically-wrapped ribbon werehelically-oriented about the exterior of stent surface. The ribbonshaped coupling member was oriented so that its FEP-coated side facedinward and contacted the exterior of surface of the stent-member. Thisribbon surface was exposed to the outward facing surface of the thinwall graft member exposed through the openings in the stent member.

[0107] Advantageously, an outer, multi-component sheath 9, formed by alongitudinally slit tube of non-adhering PTFE and an outer helical wrapof non-adhering PTFE is placed around the stent-graft-coupling memberassembly to compress the assembly onto the mandrel (FIG. 1C).Alternatively, sheath 9 may be formed by helically wrapping PTFE aroundthe stent-graft-coupling assembly without the longitudinally slit tube.

[0108] The mandrel assembly was placed into an oven set at 315° C. for aperiod of 15 minutes after which the film-wrapped mandrel was removedfrom the oven and allowed to cool. Following cooling to approximatelyambient temperature, the mandrel, as well as the cushioning layer andouter compression tube, was removed from the resultant stent-graft. Theamount of heat applied was adequate to melt the FEP-coating on theporous expanded PTFE film and thereby cause the graft and couplingmembers to adhere to each other. Thus, the graft member was adhesivelybonded to the inner surface of helically-wrapped coupling member 8through the openings between the adjacent wires of the stent member. Thecombined thickness of the luminal and exterior coverings (graft andcoupling members) and the stent member was about 0.4 mm.

[0109] The stent-graft was then folded in order to prepare it fordelivery. To accomplish this a stainless steel wire which was a coupleof inches longer than the stent-graft was inserted through the lumen ofthe stent-graft. The stent-graft was flattened and the stainless steelwire positioned at one end of the stent-graft. A second stainless wireof about the same length was placed on the outer surface of thestent-graft adjacent to the first stainless steel wire. The wires werethen mounted together into a fixture, tensioned and then rotated,thereby folding the stent-graft as shown in FIGS. 15C & D which will bediscussed in more detail below. As the stent-graft rotates it is pressedinto a “C” shaped elongated stainless steel clip in order to force it toroll upon itself. The folded stent-graft is then advanced along the wireout of the clip into a glass capture tube. A removable tether line,which is used to constrain the stent-graft in the rolled configurationfor delivery, as will be discussed in more detail below, is applied tothe stent-graft at this point by gradually advancing the stent-graft outof the capture tube and lacing the tether line through the stent-graftstructure. After this step is completed, the stent-graft is pulled offof the first wire and transferred onto the distal end of the cathetershaft or tubing for delivery.

[0110] Prior to folding, the stent-graft was cooled to about −30° C. sothat the nitinol was fully martensitic and, thus, malleable. This isdone to allow the stent-graft to be more easily folded. Cooling isaccomplished by spray soaking the graft with chilled gas such astetrafluroethane. Micro-Dust™ dry circuit duster manufactured byMicroCave Corporation (Conn) provides suitable results. The spraycanister was held upside down to discharge the fluid as a liquid ontothe stent-graft.

[0111] Deployment of the Stent-Graft

[0112] The stent-graft may be delivered percutaneously, typicallythrough the vasculature, after having been folded to a reduced diameter.Once reaching the intended delivery site, it is expanded to form alining on the vessel wall.

[0113] When a stent-graft having torsion members, as described above, isfolded, crushed, or otherwise collapsed, mechanical energy is stored intorsion in those members. In this loaded state, the torsion members havea torque exerted by the torsion members as folded down to a reduceddiameter must be restrained from springing open. The stent-memberpreferably has at least one torsion member per fold. The stent-graft isfolded along its longitudinal axis and restrained from springing open.The stent-graft is then deployed by removing the restraining mechanism,thus allowing the torsion members to spring open against the vesselwall. The stent grafts of this invention are generally self-opening oncedeployed. If desired, an inflatable balloon catheter or similar means toensure full opening of the stent-graft may be used under certaincircumstances.

[0114] The attending physician will select an appropriately sizedstent-graft. Typically, the stent-graft will be selected to have anexpanded diameter of up to about 10% greater than the diameter of thelumen at the deployment site.

[0115]FIG. 15A diagrammatically illustrates a folding sequence forfolding a stent-graft constructed according to the present invention.The stent-graft, generally designated with reference numeral 200 ispositioned about a guidewire 232 and folded into a loose C-shapedconfiguration. FIG. 15B shows a diagrammatic perspective view of theresulting folded stent-graft. FIGS. 15C & E show further foldingsequences. FIGS. 15D & F show diagrammatic perspective views of theresulting folded stent-grafts showing the rolled and triple lobedconfigurations, respectively. The rolled configuration is preferred.

[0116] FIGS. 16A-16C diagrammatically illustrate deployment proceduresfor the present invention. FIG. 16A shows an example target site havinga narrowed vessel lumen. A guidewire 208 having a guide tip has beendirected to the site using known techniques. The stent-graft 210 ismounted on guidewire tubing 212 inside outer sliding sheath 214 afterhaving been folded in the manner discussed above. The outer slidingsheath 214 binds the compressed stent-graft 210 in place until released.

[0117]FIG. 16B shows placement of the stent-graft 120 at the selectedsite by sliding the stent-graft over the guidewire all together with theguidewire tubing 212 and the outer sliding sheath 214. The stent-graftis deployed by holding the guidewire tubing 212 in a stationary positionwhile withdrawing the outer sliding sheath 214. FIG. 16B shows thestent-graft partially deployed, while FIG. 16C shows the stent-graftfully deployed after the guidewire tubing and the outer sliding sheathhave been fully retracted.

[0118] FIGS. 17A-C, 18A-C, and 19A-C show deployment variations fordeploying a stent-graft constructed according to the present invention.These methods involve the use of a control line or tether line whichmaintains the stent or stent-graft in a folded configuration untilrelease.

[0119] Referring to FIGS. 17A & B, diagrammatically representedstent-graft 302 is shown folded about guidewire 304 so that, whendeployed, the guidewire 304 is within stent-graft 302. A tether wire 306is passed through loops 308 which preferably are formed by pulling thelinking member discussed above away from the stent structure. Whentether wire 306 is removed by sliding it axially along the stent-graftand out of loops 308, the stent-graft unfolds into a generallycylindrical shape. (FIG. 17C). Referring to, FIGS. 18A & B stent-graft302 is shown in a rolled pre-deployment configuration. In this case,guidewire 304 is inside the stent. When expanded by removal of tetherwire 306, the stent-graft assumes the form shown in FIG. 18C.

[0120] FIGS. 19A-C diagrammatically show additional procedures fordeploying a stent-graft of the present invention using a percutaneouscatheter assembly 314. Referring to FIG. 19A catheter assembly 314 hasbeen inserted to a selected site within a body lumen. Stent-graft 312 isfolded about guidewire 319 and guidewire tube 318 held axially in placeprior to deployment by distal barrier 320 and proximal barrier 322. Thedistal and proximal barriers typically are affixed to the guidewire tube318. Tether wire 306 is extends through loops 308 proximally through thecatheter assembly's 314 outer jacket 324 through to outside the body.FIG. 19B shows partial removal of tether wire 306 from loops 308 topartially expand the stent-graft 312 onto the selected site. FIG. 19Cshows complete removal of the tether wire, the loops and retraction ofthe catheter assembly 314 from the interior of the stent-graft which isfully expanded.

[0121]FIG. 20 shows a close-up of a stent fold line having the familiarherringbone pattern of the preferred “sack knot” used to close the foldin the stent. This knot is the one used to hold, e.g., burlap sacks offeed grain closed prior to use and yet allow ease of opening when thesack is to be opened. In this variation, the slip line has a fixed end320 and a release end 322. Loops of the slip line pass through theeyelets 324 on the side of the stent fold associated with the fixed end320 and are held in place by eyelets 326 on the side of the stent foldassociated with the release end 322. The fixed end 320 is not typicallytied to the stent so to allow removal of the slip line after deployment.The eyelets 324 and 326 are desirable but optional. The eyelets 324 and326 may be wire or polymeric thread or the like tied to the stentstructure at the edge of the stent fold. If so desired, the loops may bedispensed with and the slip line woven directly into the stentstructure. The self-expanding stent may be deployed by pulling axiallyon release end 322 as shown by the arrow in the drawing.

[0122]FIG. 21 is a diagrammatic perspective view of a folded stent-graftusing the knot shown in FIG. 20. FIG. 21 shows the use of a single stentfold similar in configuration to those described above. As was shown inFIG. 20, the fixed end portion 320 of the slip line is associated with arow of eyelets 324 which preferably are formed by pulling local portionsof linking member 20 away from the fold line, threading the slip linetherethrough and then releasing the respective portion of the linkingmember. Alternatively, the eyelets may be tied or otherwise fixed to thestent. The release end 322 is associated with the other row of eyelets326.

[0123] Although stent-graft deployment is described using a catheter forpercutaneous delivery, it should be understood that other deploymenttechniques may be used. The folded stent-graft may also be deployedthrough artificial or natural body openings with a sheath or endoscopicdelivery device, for example, and perhaps, without a guidewire.Similarly, the stent-graft may be delivered manually during a surgicalprocedure.

[0124] The stent-graft of the present invention may be used, forexample, to reinforce vascular irregularities and provide a smoothnonthrombogenic interior vascular surface for diseased areas in bloodvessels, or to increase blood flow past a diseased area of a vessel bymechanically improving the interior surface of the vessel. The inventivestent-graft is especially suitable for use within smaller vesselsbetween 2 mm and 6 mm in diameter but is equally suitable forsignificantly larger vessels. The inventive stent-graft may beself-expanded so that it may be percutaneously delivered in a foldedstate on an endovascular catheter or via surgical or other techniquesand then expanded. The stent-graft construction described above alsoprovides a variable length stent-graft. This is especially advantageousduring implantation procedures.

[0125] Currently, it is difficult for a physician to accuratelydetermine anatomical distances due to vessel tortuosity in differentplanes which often occurs in aorta/iliac aneurysmal disease. Also, it isimportant for the physician to accurately measure distances when placingan endovascular stent-graft so the entire aneurysmal length is covered,yet important vessel branches are not occluded. The stent-graft designof the present invention allows the physician to adjust its lengthduring deployment allowing more accurate placement of the device.

[0126] The following example illustrates the steps involved in placing avariable-length stent-graft into a patient's anatomy. In this example,stent-graft is a single tubular design, placed into the thoracic aorta70, and will be located between the renal arteries and the T-7 artery.The direction of deployment will be from renals ‘upstream’ to the T-7artery. The device will be supplied in its longest state with shorteningcapability during deployment (the inverse where a copressed stent-graftis deployed also is possible).

[0127] The physician estimates the length required, and chooses a devicewhich is at least as long, and usually slightly longer than theestimated length.

[0128] The stent-graft is inserted through an introducer as isconventional in the art. It is advanced until its distal ends 2 a islocated as desired near the renal arteries (72) (FIG. 22). At thispoint, the proximal end of the stent-graft would be located at or pastthe T-7 artery (74).

[0129] The stent-graft deployment is initiated slowly, distal toproximal (‘downstream to upstream’) (FIG. 23) while watching theproximal end location on fluoroscopy.

[0130] As needed, the delivery catheter 76, which is of conventionalconstruction, would be pulled toward the operator, shortening thestent-graft to keep the proximal end in the correct location. Thisshortening can occur as long as the portion of the stent-graft beingcompressed is within the aneurysm 78.

[0131] Once the proximal end is correctly located (FIG. 24), the stentgraft is fully deployed, and the delivery catheter is removed (FIG. 25).

[0132] Throughout this application, various publications, patents andpatent applications are referred by an identifying citation. Thedisclosures of these publications, patents and published patentapplications are hereby incorporated by referenced into thisapplication.

[0133] The above is a detailed description of a particular embodiment ofthe invention. The full scope of the invention is set out in the claimsthat follow and their equivalents. Accordingly, the claims andspecification should not be construed to unduly narrow the full scope ofprotection to which the invention is entitled.

What is claimed is:
 1. A stent-graft comprising: a stent member havingan inner surface and an outer surface; a generally tubular graft member;and a ribbon covering only a portion of at least one of the inner andouter surfaces of said member and securing the stent member and graftmember to one another.
 2. The stent-graft of claim 1 wherein said stentmember comprises a tubular member.
 3. The stent-graft of claim 2 whereinsaid stent member comprises multiple tubular members.
 4. The stent-graftof claim 1 wherein said stent member comprises a first member havingundulations and being arranged in a helical configuration with multipleturns.
 5. The stent-graft of claim 4 wherein said ribbon is arranged ina helical configuration with multiple turns, each turn being spaced froman adjacent turn.
 6. The stent-graft of claim 5 wherein said spacingbetween said turns is uniform.
 7. The stent-graft of claim 5 whereinsaid ribbon covers a portion of said undulations.
 8. The stent-graft ofclaim 5 wherein said ribbon is interwoven into at least one of saidundulations.
 9. The stent-graft of claim 5 further including a linkingmember threaded between adjacent turns to maintain undulations inadjacent turns generally in-phase with one another.
 10. The stent-graftof claim 9 wherein a number of said undulations are configured to permittherein unrestrained movement of an undulation generally in-phasetherewith.
 11. The stent-graft of claim 5 wherein a group of saidundulations forms a sinusoidal curve.
 12. The stent-graft of claim 5wherein said ribbon has a width less than or equal to about two-thirdsthe average amplitude, measured peak-to-peak, of one of saidundulations.
 13. The stent-graft of claim 12 wherein said ribbon has awidth less than or equal to about three-fourths the average amplitude,measured peak-to-peak, of one of said undulations.
 14. The stent-graftof claim 1 wherein said graft member has an average thickness of lessthan or equal to about 0.006 inch.
 15. The stent-graft of claim 14wherein said ribbon has an average thickness of less than or equal toabout 0.005 inch.
 16. The stent-graft of claim 1 wherein said graftmember comprises porous expanded polytetrafluoroethylene.
 17. Thestent-graft of claim 16 wherein said ribbon comprises porous expandedpolytetrafluorethylene.
 18. The stent-graft of claim 1 wherein saidgraft member comprises radiopaque fibers.
 19. The stent-graft of claim 1wherein said stent member comprises nitinol.
 20. The stent-graft ofclaim 1 wherein said ribbon is adhesively bonded to said graft member.21. The stent-graft of claim 1 wherein said ribbon has a generally flatportion that faces said graft member.
 22. A stent-graft comprising: astent member having an inner surface and an outer surface; a generallytubular graft member having an inner and an outer surface, one of saidstent and graft members surrounding at least a portion of the other; anda ribbon interconnecting less than entirely one of said inner and outersurfaces of said graft member to said stent member.
 23. The stent-graftof claim 22 wherein said ribbon is arranged to include multiple helicalturns, at least one of said turns being spaced from a turn adjacentthereto.
 24. The stent-graft of claim 22 wherein said ribbon has agenerally flat portion that faces said graft member.
 25. The stent-graftof claim 22 wherein said stent member is tubular, said stent and graftmember are generally coaxial, and said graft member is disposed in saidstent member.
 26. A stent-graft comprising: a stent member having aninner surface and an outer surface, said stent member including a firstmember and a second member, said first member being arranged in ahelical configuration with multiple helical turns, said second membercoupling adjacent helical turns; a generally tubular graft member havingan inner surface and an outer surface, one of said stent and graftmembers surrounding at least a portion of the other; and a couplingmember coupling less than entirely one of said inner and outer surfacesof said graft member to said stent member.
 27. The stent-graft of claim26 wherein said first member includes multiple undulations, each havingan apex, said coupling member is helically arranged and spaced from saidapexes to form therewith respective openings, said apexes beingconfigured to permit unrestrained movement of said second member withinsaid openings.
 28. A stent-graft comprising: a generally tubular stentmember having inner and outer circumferences, said stent memberincluding a first member and second member, said first member beingarranged, in a helical configuration with multiple helical turns andhaving multiple undulations, each undulation having an apex, said secondmember being threaded through adjacent apexes in adjacent turns tomaintain undulations in adjacent turns generally in-phase with oneanother; a generally flat ribbon helically arranged and disposed tocontact at least one of said inner and outer circumferences of saidstent member and forming multiple windings spaced from one another; anda generally tubular graft member disposed within said stent memberportions of which are secured to said ribbon.
 29. The stent-graft ofclaim 28 wherein said helically wound ribbon is generally spaced fromsaid apexes and forms therewith respective openings, said apexes beingconfigured to permit unrestrained movement of said second member withinsaid openings.
 30. A method of deploying a stent-graft comprising thesteps of: placing a first end of a variable length stent-graft having aninner graft member, an outer, helically wound stent coupled to saidgraft member by a helically wound ribbon with spaced apart turns, at afirst site in a mammal; moving the second end of the stent-graft towarda second site in a mammal; lengthening the stent-graft if the second enddoes not reach the second site; and shortening of the stent-graft if thesecond end extends beyond the second site.
 31. A process for making astent graft comprising: (a) placing a graft around a mandrel; (b)positioning a stent having undulations around said graft; and (c)covering a portion of said stent and graft with a coupling member havinga flat surface, to form a stent-graft assembly.
 32. The processaccording to claim 31 further comprising the step of: (al) prior to step(a), placing a cushioning layer around the mandrel.
 33. The processaccording to claim 31, wherein said covering step comprises helicallywrapping the coupling member around the stent whereby adjacent turns ofthe helically wrapper coupling member are spaced from one another. 34.The process according to claim 32, wherein said covering step compriseshelically wrapping the coupling member around the stent whereby adjacentturns of the helically wrapper coupling member are spaced from oneanother.
 35. The process according to claim 32 wherein the couplingmember is bonded to an outer surface of the graft.
 36. The processaccording to claim 31 further comprising the step of: (d) placing asheath around the assembly of step (c) to form a compressed assembly.37. The process according to claim 35 further comprising the step of:(e) heating the tensioned assembly of step (d) to bond the couplingmember to the graft.
 38. The process according to claim 34 furthercomprising: (d) placing a tubular sheath having a longitudinal slitaround the assembly of step (c); and (e) helically wrapping a filmaround the sheath to compress the assembly.
 39. The processing accordingto claim 36 wherein the sheath includes a helical wrapping of PTFE film.40. The stent-graft of claim 16 wherein one side of said ribbon has acoating of a fluorinated ethylene propylene polymer.